WASHINGTON -- "How's My Driving?" stickers were once the butt of jokes, considered "Big Brother" on the road.

Today, the decals are affixed to hundreds of thousands of 18-wheelers and other commercial vehicles rolling across America. And rising cell phone use has resulted in an increase in calls to phone numbers displayed on the vehicles -- and the occasional firing of an unsafe driver.A decade old, "How's My Driving?" gets mixed reviews.

"I'm not scared of answering to safety," said Dan Hallford, a trucker from Montgomery, Ala., who thinks they're a good idea.

But Wallace Harris, a driver from Vernon, Ala., doesn't think they make the roads any safer.

"You get too many people getting mad at truckers and just calling in," Harris said. "People will call in, and I will have no way to defend myself."

Some companies answer their own complaint calls from motorists. Others hire firms like FleetSafe or DriverCheck, both in Atlanta, Safety Alert Network in Metairie, La., and DriversAlert in Boca Raton, Fla., to collect the comments and compile incident reports.

Convinced they make drivers more safety-conscious, some insurance companies offer discounted premiums to fleets whose trucks carry the decals. Fireman's Fund Insurance Co. pays for monitoring 30,000 commercial vehicles operated by companies it insures, says Paul Farrell, loss control manager.

And it pays off, he said: "Fleets that use the program have 20 percent fewer accidents."

Still, skepticism surrounds "How's My Driving?" programs.

"The drivers say 'Isn't this Big Brother watching me?' " Farrell said. "The general public -- they may be a little bit wary of giving their name and phone number. That information is protected, but if somebody's not clued in to how the whole system works, they might feel like, 'Gee, is there going to be a nasty, crazy driver knocking on my door tomorrow?"'

That misconception didn't dissuade David Reiner from grabbing a cell phone in his pickup truck and calling a toll-free "How's My Driving?" number on the back of a delivery van that braked suddenly on a busy road in Southern California.

Reiner says the van driver glared at him in his rearview mirror, then stomped on his brakes again -- and again -- and again.

"I don't know what I did to make him angry -- but he kept slamming his brakes in front of me. It almost seemed like he was trying to get me to rear-end him," Reiner of Arleta, Calif., told a representative of FleetSafe.

FleetSafe could not disclose what, if anything, happened to the van driver. But to help validate complaints, the company asks motorists detailed questions about the incident being reported.

FleetSafe's call center asked Reiner: What type of vehicle was it? ("A white van.") Was the weather clear and dry? ("A little cloudy.") Was traffic light or heavy? ("Moderate.") His complaint then was faxed to the delivery company, which would decide whether to discipline the driver.

Still, safety directors at some trucking companies worry the decals give motorists a venue to vent frustration.

Bored drivers sometimes call in petty complaints, says Donna Eastman, safety director for LaValle Transportation Inc., of Potsdam , N.Y., which has 50 trucks displaying the company's phone number.

"If a truck passes their car and it's raining and they get their windshield all yucked up, people will call and say 'Well, he was really speeding.' " Eastman said. "Sometimes you get somebody who has a grudge against a driver and are just calling to get them in trouble."

That's the exception, not the rule, says Ken Rees, national sales manager for DriverCheck. He says trucking companies tell him that only a handful of complaints are false, vindictive or invalid.

"Ninety percent of the incidents are caused by only 10 percent of the drivers," Rees said. "The idea is to pinpoint that small body of folks and change their behavior through counseling and safety programs -- before an accident occurs."

More than 90 percent of the drivers are never targets of a complaint, says FleetSafe president Richard Lea. About 85 percent of the calls concern such things as tailgating, improper lane changes, speeding or running stop lights or signs, he says, while 10 percent are compliments and 5 percent report emergencies or other concerns.

Truck companies use the reports to spot problem drivers, says Jim Reali, regional safety manager for SYSCO Corp., a Houston-based company with decals on about 3,000 of its 7,000 trucks. He says the company, which received 435 incident reports last year, does not usually fire a driver for one complaint.

"When we start seeing a trend on one employee, he is given a reprimand first," Reali said. "Normal policy would be to make sure he's retrained or goes through a safe driving course."